Mojtaba Karimaei Tabarestani - Department of Civil Engineering, Faculty of Geotechnical and Water Engineering, Shahid Rajaee Teacher Training University, Lavizan, Tehran, Iran.
Atabak Feizi - Department of Civil Engineering, Faculty of Engineering, University of Mohaghegh Ardabili, Ardabil, Iran.

In this study, a probabilistic method was proposed to determine the stable riprap as a scour control measure downstream of a stilling basin, using the Monte Carlo Simulation Technique. The Kan diversion dam in Iran was selected as a case study, and various uncertainties in the model, including hydraulic parameters for different design flood events, were taken into account during the analysis. Moreover, the relationship between the probability of failure, structure lifespan, and riprap sizing was also investigated. The results indicated that the estimates for riprap data followed a normal distribution. By utilizing the characteristics of this distribution, such as the mean and coefficient of variation, the stable riprap sizes were calculated based on the desired probability of failure and the structure lifespan. For instance, when considering a ۵% probability of failure, the riprap size was determined to be ۰.۲۰۳ m for a ۵۰-year design flood. Similarly, for larger floods, such as a ۲۰۰-year design flood, the riprap size needed to be increased by ۶۵%. Furthermore, as the structure lifespan increased from ۲۵ years to ۲۰۰ years, the riprap stone size saw an approximate ۲۵% increase for a ۲۰۰-year design flood.

Stilling basin, Scour countermeasure, Riprap size, Probabilistic framework, Structure life span